1. Field of the Invention
The present invention relates to an improved technique for blowing conductive links by the application of radiant energy thereto.
2. Description of the Prior Art
Fusible conductive links are commonly used in solid state device production, including, for example, integrated circuit (IC) production. One type of fusible link is normally conductive, and is rendered non-conductive (i.e., "blown") by one or more pulses of laser energy directed at the link. The laser energy melts and/or vaporizes the conductive link material, thereby removing it from the conductive path. The conductive material may be a metal, for example aluminum, or alternately may be doped polysilicon or a metal silicide. The links are typically formed by patterning a layer of the conductor that is formed on a dielectric layer, typically silicon dioxide or a glass. It is further known to utilize multiple conductive interconnect levels having links in each level. For example, in one conventional process, a first conductive layer of doped polysilicon is deposited on a layer of silicon dioxide overlying a silicon substrate. (For increased conductivity, a metal may optionally be reacted with the top portion of the polysilicon to produce a silicide surface layer in the so-called "polycide" structure.) The polysilicon layer is then patterned to form a first interconnect level, which includes portions of the pattern at various locations intended to serve as links. A glass layer is then deposited, and a second conductive layer of aluminum is deposited and patterned to form a second interconnect level. Portions of the aluminum pattern also serve as links. A laser is subsequently used to blow the desired links in either or both of the two conductor levels.
One well known application for blowing links is in the programming of redundant rows and columns for integrated circuit memory arrays; see, for example, U.S. Pat. No. 4,228,528 co-assigned with the present invention. Another use is for programming logic chips that initially have a large number of identical logic gates connected together. By blowing the links wherever it is desired to remove a "short" from the final circuit design, a large variety of logic circuits may be implemented with relatively fast turn-around time. Still other possible uses include programming wafer scale integrated circuits, wherein links are blown to configure the active elements of the circuit in a desired pattern, or to substitute good circuits for defective ones.
The reliability of blowing links affects the overall yield of good integrated circuits. The reliability of link blowing is especially important when the number of links to be blown on a given IC is large. Therefore, methods of improving the ease and reliability of blowing links are desirable.